Electrolytic method of producing finely divided copper



ELECTROLYTIC METHOD OF PRODUCING FINELY DIVIDED COPPER Filed July 22, 1968 2 Sheets-Sheet 1 V N h V N l MATT/105W a ZQ u/WE BY 6% 1970 M. c. BLUME 3,3,

ELECTROLYTIC METHOD OF PRODUCING FINE-LY DIVIDED COPPER Filed July 22, 1968 2 Sheets-Sheet 2 *h fa K/ 20 p INVENTOR. MAT/1967M C, 2&0/145 United States Patent U.S. Cl. 204 13 Claims ABSTRACT OF THE DISCLOSURE A method of electrolytically producing copper powder wherein an electrolysis bath consisting essentially of a pyrophosphate soluble in water which produces an alkaline solution and a tetravalent pyrophosphate anion concentration of at least one-quarter percent by weight.

This application is a continuation-in-part of my copending application Ser. No. 500,626 filed Oct. 22, 1965, now Pat. No. 3,394,063 issued July 23, 1968.

This invention is that of a process of electrochemically producing finely divided copper from various forms of starting copper metal used as an anode in an electrochemical cell to provide at its cathode finely divided copper particles, as small as, for example, all smaller than 60 mesh per square inch with various amounts of the different smaller sizes down to smaller than 325 mesh.

More particularly the method of the invention involves obtaining such finely divided copper particles by passing an electric current through the starting copper metal while it is submerged as the anode in an alkaline aqueous bath having dissolved in it a water-soluble pyrophosphate, through which bath the current passes to a cathode inert to the bath. Such bath is prepared free of any electrolyte which forms a water-soluble copper salt and thus would enable direct electrodeposition of copper as a strongly adherent electroplate.

Heretofore finely divided copper was prepared by several different methods, for example, (i) dissolution of copper in dilute sulfuric acid to produce a suitable aqueous copper sulphate solution and then immersing in that solution a sufiicient quantity of a metal higher than copper in the electromotive series, such as iron, aluminum, magnesium or zinc, which entered into solution and displaced the copper in finely divided form; (ii) gaseous reduction, as by hydrogen at elevated temperatures, of finely divided copper oxides obtained by any of various methods, or (iii) atomization of falling molten copper by contact with a high velocity stream of compressed inert gas, steam, or water. The best resulting copper powder analyzed 99.6%.

All of such earlier methods have several obvious disadvantages, for example, in requiring some one or more of various expendable reagents and unduly high power consumption, resulting in high cost. These and various other disadvantages and shortcomings of the prior methods are overcome by the process of the invention.

Thus, a valuable feature of this invention is that it enables easy and ready production of high quality (at least 99.7% Cu) finely divided copper from any type of larger than finely divided copper starting metal, even many forms of copper scrap.

A further feature of the invention is its low operating cost in that it requires little labor attention except at loading and unloading.

Another feature of the invention is the low cost of its electrolyte bath because of the pyrophosphate electrolyte is not consumed in use, and loss by dragout can be kept exceedingly low.

3,539,458 Patented Nov. 10, 1970 Yet another feature of the process is the stable character of the electrolysis bath which requires no adjustment during operation.

Still a further feature of the invention is its ready provision of the finely divided copper in a state from which it readily is placed in saleable form and at good value.

In this specification and its accompanying claims, the expression copper starting metal, sometimes referred to as larger size copper, is intended to cover any size pieces of copper, say, larger than 60 mesh, which readily can be handled as starting material to serve as the copper anode in the electrochemical operation conducted in the aqueous water-soluble pyrophosphate bath used in the method of the invention; for example, any available grades of copper sheet, bars or rods which by themselves can serve as anodes, or various types of scrap copper such as punchings from copper sheet or the waste skeleton remaining after punching various forms from copper sheet, as well as copper rejects of such and other operations, or waste copper Wire, or even copper spirals from boring and drilling operations, and even from screw machine operation, and also copper wastes from other machining operations, as well as any other waste copper, all of which latter smaller copper pieces can be used, for example, by loading them into anode bags inert to the alkaline bath.

Considered broadly, the process of the invention comprises submerging the starting copper metal in an aqueous alkaline bath having dissolved in it a readily water-soluble pyrophosphate, and passing an electric current through the copper metal as the anode into and through the bath and to a cathode which is inert to the bath. The passage of current is continued conveniently until substantially all of the starting copper metal has been consumed. It is advantageous that the bath be free of any electrolyte which can solubilize copper and allow it to be deposited on a cathode as an adherent and continuous electroplate.

The process will operate at a concentration of as little as one quarter of a percent or less of the tetravalent pyrophosphate anion (that is P O in the bath, but at that level the operating time is quite long. Time production improvement is seen in building up to a pyrophosphate anion concentration of 0.75 percent. However, it is advantageous to operate with the pyrophosphate anion concentration at from about 1.5 to about 5.5 percent.

It is beneficial to provide that anion by dissolving an alkali metal or ammonium pyrophosphate in the bath, and advantageously by using tetra-potassium pyrophosphate (i.e. K P O or tetra-sodium pyrophosphate (i.e. Na.,P O or mixtures of any thereof. So far as presently indicated, the potassium salt appears to perform much better than the sodium salt. The process will operate with any of these dissolved even to saturation, but nothing is to be gained by using such high concentration.

At the high levels approaching saturation, the viscosity increases and dragout is greater although it can be kept at a minimum by rinsing any removable part or parts while being held above the bath when removed from it. Also any pyrophosphate electrolyte solution filtered from the removed sludge containing the finely divided copper can be returned to the bath. There likewise can be returned to it even the concentrated washing resulting from the earliest amount of water used to wash the filtered sludge particularly if a highly concentrated bath was used.

For the most part, it is beneficially practical not to use the water-soluble pyrophosphate in a concentration above that which will give greater than about 12 percent of pyrophosphate anion, although as stated the process will operate at concentrations above that. Any such higher concentration can be used so long as the bath viscosity is not so great as to cause unduly high dragout.

It is possible with suitable adjustment of other conditions, such as voltage, current density, pyrophosphate anion concentration, or temperature, to operate the method with the alkalinity of the bath at as low as pH 9 and up to about pH 9.5. However, it is advantageous that the pH be above 9.5 in that the rate of finely divided copper production is increased, for example, to about fivefold by maintaining the bath a pH of from about 10 to about 10.8. Thus, it is advantageous to operate at a pH from about 10 to about 11. The rate begins to decrease when the pH is at about 11.2, and at above about pH 115 there does not appear to be any noticeable finely divided copper production.

These pH levels are by pH meter. The pH can be ad justed to the desired level, in preparing the :bath, by adding sufiicient strong alkali hydroxide such as potassium or sodium hydroxide.

While the process operates at ambient temperature, it should be operated at elevated temperature beneficially from about 130 to about 190 F., still better between about 150 and 170 and, so far as presently indicated, advantageously in the neighborhood of about 160 F.

As to voltage, it is beneficial, so far as presently indicated, to operate at below about 7 volts and advantageously at from about 3 to about volts. So far as presently indicated, it is beneficial for the current density to be under about 2 amperes per square foot and advantageous for it to be under one ampere per square foot. Much depends on the variation in size of the starting copper sheets, bars or rods to be used, as well as the various different sizes of the pieces in the scrap loads. In a number of the better runs the current density appeared to be between about 0.15 and 0.1 ampere per square foot.

The cathode can be any suitable conductor so long as it is inert to the alkaline bath. Generally it is advantageous to conduct the process in an iron tank. Such tank then can serve as the cathode as can also any other metal tank which is inner to the alkaline bath under the operating ocnditions and is a conductor, with the starting copper metal suitably insulated from the tank. Steel or iron sheets, bars or rods can serve as good cathodes, as can also carbon or graphite cathodes.

During the operation of the process, the passage of the current removes copper from the starting copper metal; and the resulting produced finely divided copper only loosely adheres to the cathode. As the thus loosely adhering copper builds up on the cathode, of its own weight it drops to the bottom and what still adheres to the cathode readily is removed from it when needed by light scraping, and generally where it can be done merely by lightly striking the cathode.

The thus obtained finely divided copper need not be removed at the end of the individual run but rather can be allowed to accumulate at the bottom of the bath tank with any amount of it which fell to the bottom during the operation, or was accumulated there from the prior run or runsto be removed in suitable manner when desired or when its depth is so great as soon to interfere with the movement of any part of any apparatus rotated in the tank.

The finely divided copper product of this electrochemical procedure is removed from the bottom (primarily about the cathode end when using a stationary anode) of the bath, where it has accumulated, as a sludge. The latter then is Washed with water (lukewarm to hot) till desirably free of adhering electrolyte, by any suitable method depending on the volume of material being handled. For example, a large Biichner filter can be used as for pilot batches, or, after stirring up the sludge with a limited amount of Water into a conveniently handable slurry, the latter can be fed through a plate filter press or if of suitable volume over a continuous filter.

More often, the finely divided copper obtained after thus merely washing the sludge varies in color from light to dark brown. For certain uses this washed product then is dried preferably in a non-oxidizing atmosphere such as under vacuum or a blanket of carbon dioxide or nitrogen or suitable mixture of them.

However, if the finely divided copper is to be sold for uses where even the slight amount of oxide coating on the washed product is undesirable, then the washed finely divided copper is dried under an atmosphere of hydrogen and preferably at an elevated temperature in a suitable apparatus and under operating conditions (temperature, etc.) as are known in the art, for example, as shown by the American Chemical Society Monograph series No. 122 Copper The Metal Its Alloys And Compounds, Rheinhold Publishing Corporation, New York, N.Y., 3rd printing (1960) page 349.

The aqueous alkaline bath can be used, as indicated, quite indefinitely, for the water-soluble pyrophosphate is not destroyed in use and dragout losses are insignificant. That is so because they are kept at a minimum by rinsing any removed element or apparatus with water and allowing the rinsings to run back into the tank, and returning filtrate and possibly also washings from the removed finely divided copper sludge, as mentioned above. Thus, only insignificantly small amounts of water-soluble pyrophosphate need be added as indicated by the liquid level of the tank, or when by checking the specific gravity of the bath at suitable times.

In carrying out the process of the invention with the starting copper metal in the form of rods, bars or sheets, any of the-m can be suspended for immersion in the bath, from a suitable horizontal anode suspension bar, the outer ends of which if resting on the top edges of the tank are to be insulated from it if the tank is to serve as the cathode. Similarly, if the starting copper metal is scrap such as drilling or boring or screw-making coils or other machine shop or other source waste too small to be retained by perforations as low as an eighth or sixteenth of an inch or so in a cylindrical retaining vessel, it can be loaded into suitable elongated bags resistant to the alkaline bath such as the anode bags of cotton or other material resistant to the alkalinity of the bath. With both of these types of anodes, the process is carried out in a still tank.

However, with larger sized scrap starting copper material, it is advantageous to load such scrap into a perforated tumbling barrel or drum mounted for rotation on a horizontally axially positioned electric conductor metal shaft (resistant to the alkalinity of the bath) to serve as the anode. The latter is contacted by the scrap while the barrel is submerged in the tank and rotated about the shaft, the outer ends of which are insulated from the tank which, if made of iron or other suitable conducting metal, serves as the cathode. Such practical operation is exemplified by the apparatus arrangement shown in the accompanying drawings wherein:

FIG. 1 is a longitudinal side elevation of the apparatus, 'With part of a tank wall in broken section exposing the tumbling barrel (in this case as two units) and its shaft and supports, etc.;

FIG. 2 is a top plan view;

FIG. 3 is a front to rear vertically transverse section on an enlarged scale, along the line 3-3 of FIG. 1 and viewed in the direction shown by the arrows;

FIG. 4 is a fragmentary foreshortened longitudinally vertical sectional view through the dual barrels and their supports along the line 44 of FIG. 3 and viewed in the direction shown by the arrows;

FIG. 5 is a fragmentary partial sectional view through the brushes encircling the shaft and at the end of the conductor, along the line 5-5 of 'FIG. 4 as viewed as directed by the arrows; and

FIG. 6 is a fragmentary sectional view along line 66 of FIG. 4 looking in the direction of the arrows.

The drawings show the steel, bath-holding tank 11, in which the twin or dual perforated Wall drums or barrels 12 and 12a are mounted in tandem for rotation about their common steel shaft 14 supported at its outer ends in opposed nylon insulator bearings 15. These bearings are carried in vertical suspension arms 16 depending into the tan-k with their lower end spaced upwardly away from the tank bottom.

The upper ends of these arms 16 are secured respectively to the opposed ends of a pair of parallel horizontal channel iron carriers 18. The latter extend over the length of tank 11 and are supported spaced upwardly away from contact with it by a pair of parallel widely horizontally spaced apart hoist-engagement rods 19, each of which extends through both of carriers 18 and has its outer ends seated in the grooves in the top of its respective pair of opposed insulator-separators 20 resting on encircling flange 21 of tank 11.

Motor 23 drives shaft 14 by chain belt 24 riding over motor sprocket 29 and shaft sprocket 30. Current from a power source and rectifier (both not shown) to conductor 25 enclosed in its insulator-sheath 26 flows through the pressure-spring clamped brushes 28 to anode shaft 14. Shaft sprocket 30 is insulated from shaft 14 by centrally interposed nylon insulator ring 32 encircling the shaft and fixd to rotate with its annularly-encircling rest of sprocket 30.

Likewise, each of the end walls of each of the dual drums 12 and 12a is insulated from shaft 14 by a similar centrally interposed nylon insulator ring 33, 33a, and 34 and 34a. Each of the drums can be constructed of suitably strong material for the load to be carried in them, for example, sheet steel (which may be stainless) or other suitable metal, or Wire cloth of suitable mesh (e.g. 80 or even as small as 325 per square inch), or strong enough or suitably strengthened plastic or other non-conductor material. They can be cylindrical or advantageously polygonal, e.g. octagonal (as in FIG. 3).

As shown in FIG. 6, one or more extension conductors, suitably longitudinally spaced apart along, extend radially outwardly from, shaft 14 to make electrical contact with the copper charge in the drum or drums 12 and 12a when the copper is so far consumed that its level is below and out of contact with the shaft. Beneficially each such extension conductor 40 can consist of a collar 41 encircling shaft 14 in electrical-conductivity contact but loose enough not to rotate with it under the weight of chain 42 depending from it.

Positioning pins 43 restrain collar 41 from moving axially along the shaft. A similarly swingable conductor rod can replace chain 42. The outer ends of any two or more of such rod or chain 42 can be joined by a conductor rod or bar held by them parallel to the shaft. So long as drum 12 or 12a is insulated from shaft 14 or is of electrical non-conductor composition, any of the conductors 40 may touch the interior of its peripheral wall. Otherwise, it is desirable that rod or chain 42 terminate at a length to avoid contacting that interior wall.

The peripheral walls of the drums are perforated advantageously all over (by perforations and should permit access for loading and unloading by suitable doors 36 mounted on scabbard hinges and locked by easily closeable and openable catches such as wing-nut tightenable hinged swing-bolts to allow quick unlatching and removal (if desired) of the doors for unloading the drums and also quick replacement and locking of the doors after loading.

As already indicated, steel tank 11 serves as the cathode, and a (negative) conductor 37 leads away from it to complete the circuit. With drums 12 and 12a positioned as seen in FIG. 3, the entire treating assembly including them, shaft 14, its suspension arms 16 can be lifted out of tank 11 by engaging hooks from hoist chains under the two parts of each of hoist-engagement rods 19 just outside of both channel iron carriers 18. The entire assembly thus lifted out of tank 11 then is let down with the lower ends of suspension arms 16 to rest on the plant fioor. If the drums are of such capacity that the load on the shaft may be too great, an intermediate suspension arm 16 with a nylon insulating bearing 15 can be included midway between the drums. Then shaft sprocket 30 and brushes 28 are to be set sufiiciently further apart.

With the entire treating assembly thus out of tank 11, the doors of drums 12 and 12a can be removed to allow loading copper scrap into them. A heater (not shown), insulated against receiving current from shaft 14 through the solution used in the tank, is placed conveniently effectively located in tank 11 to enable heating the solution to the selected operating temperature and to maintain it there.

A fairly practical size apparatus as seen in the drawings has a tank about 15 feet long by 5 feet high by 3.5 to 4 feet wide with each drum about 7 feet long and 25 inches in diameter (with adequate clearance on all sides) with a capacity to handle at least 1500 to about 3000 pounds of scrap per drum per run.

The method of the invention and operation of apparatus are illustrated, by, but not limited to, the following example:

800 pounds of anhydrous tetra-postassium pyrophosphate (K P O are charged into a tank 11 of the foregoing dimensions (width 3.5 feet), and dissolved by pumping in 1500 gallons of water (providing a solution of very nearly 6% concentration) while the heat is on to raise its temperature to about 160 F. The pH of the solution is adjusted to 10.5 (by meter). In the meantime a ton of scrap copper was loaded into each of the dual drums of the apparatus (as shown in the drawings) and having the above-noted dimensions.

The entire drum and carrier assembly is raised and set in place with the drums submerged below the electrolyte solution level in the tank. The electrolysis current is turned on to pass a current of about amperes at a voltage of 4.5 through the bath while motor 23 rotates the drums 12 and 12a at 10 rpm. The copper is seen to be substantially completely consumed within a half hour to an hour and a half and up to two hours (time variation occurs according to the thickness of the starting copper scrap loaded into the drums or anode bags, or of the copper sheets, bars or rods used as anodes when operating the method in a still tank).

The finely divided copper particles deposit loosely adherently on the walls of tank 11 (or on any sheet, bar or rod cathodes when the tank does not serve as the cathode) and drop down as finely divided copper particles forming a metal sludge over the bottom of the tank, on striking its Sides (or any other cathodes used). The current then is shut off, the entire assembly of drums and carriers raised out of the bath and held above it while a water spray rinses dragout solution from the drums, any remaining scrap content, the shaft and suspension arms 16 back into the bath, beneficially to raise its level back to where it was before the assembly was submerged in it.

The assembly then is moved aside and lowered to the plant floor level, and the consumed scrap is replaced by a new load of scrap, with which the operation of the example is repeated. Such operation is repeated again and again.

The operation conditions can be varied within the ranges disclosed further above as the character of any of the different types of scrap may require. The K P O may be replaced in part or as a whole by another applicable pyrophosphate, as disclosed hereinabove, for example, tetra-sodium pyrophosphate. The pH can be checked from time to time and be adjusted with alkali metal hydroxide when necessary. Small amounts of the desired pyrophosphate can be added when, after many runs, test of the specific gravity of the bath shows that more of that substance may be needed to bring its concentration back to a desired level.

Two complete assemblies can be used so that a loaded one can be lowered to submerge its drums in the bath when a finished rinsed one is removed to be unloaded and refilled. It is also helpful to have a wider bath and to have two separate sets of drums submerged and at different stages of completion while a third one is outside being emptied and refilled.

The process also is carried out in a still tank, wherein stationary anodes of sheets, bars or rods of the starting copper metal are used instead of the removable rotatable copper scrap-containing drums, under the same operating conditions and in about the same way (excluding the use of the drum apparatus) as described in the foregoing illustrative example. To avoid unnecessarily extending the specification, that example then is to be considered as if repeated here in full with that drum apparatus replaced by an anode holder supporting stationary anodes of copper sheet, bars and rods respectively, and likewise anode bags containing small pieces of copper waste such as earlier described, submerged in the electrolyte bath.

The following screen analysis of the product of a specific run merely is illustrative of the range of particle size distribution in the finely divided copper product of the method of the invention, after washing and drying (without using hydrogen), and after all passed through the 60 mesh (per square inch) screen (with openings of 0.0097 inch).

Held on mesh screen Weight percent 80 (openings 0.0069 inch) 24.0 100 11.4

through 325 19.0

The product can be used without size separation or reduction if so suitable to the customers needs. If a specific size range is required, the product can be screened or reduced to a required smallest size by comminution by any readily available grinding or hammer mill such as the Fitzpatrick adaptation of the hammer mill.

The washed product dried at elevated temperature (such as 1000" to 1300" F.) under hydrogen presents the pink color of freshly clean copper. It analyses 99.7 percent and over, even when obtained from scrap copper Whose analysis varies from 98 to 99% Cu and up to 99.5%, as compared to 99.6% Cu in the finely divided copper product of the prior methods.

The process can operate also on lacquered starting copper metal and result in removing the lacquer coating without prior treatmentand Works similarly with oily and greasy starting copper metal.

The tank can be made of steel, or any other conductor metal, or alloys of them, so long as it is an electrical conductor, and advantageously a structural metal higher than copper in the electromotive series and inert to the alkaline electrolysis conditions.

The perforated walls of the tumbler drum can be made of some other suitably strong enough metal or non-metal so long as it is inert to the alkaline electrolysis bath. The perforations in the drum can be of any size suitable for the particular type of scrap to be handled in it, for example, down to one sixteenth inch, or beneficially the sizes available from using wire cloth, say, of 60 mesh or smaller, for the peripheral walls of the drum or as a liner for it.

While the invention has been explained by detailed description of certain specific embodiments of it, it is understood that various modifications or substitutions can be made in any of them within the scope of the appended claims which are intended also to cover equivalents of the specific embodiments.

What is claimed is:

1. The process of preparing finely divided copper from starting larger copper metal, which method comprises (a) submerging said starting copper as an anode in an aqueous alkaline electrolysis bath having a pH of from 9 to about 11.5 and whose principal electrolyte consists essentially of a pyrophosphate soluble in Water to give an alkaline solution and a tetravalent pyrophosphate anion concentration of at least about one-quarter percent by weight, said solution being free of any solute which can form a water-soluble salt of copper and enable its electrodeposition as a strongly adherent electrodeposit under the operating conditions;

(b) passing an electric current through said anode into and through said bath to a cathode inert to said bath under the operating conditions; and

(c) separating the resulting finely divided copper from said bath.

2. The process as claimed in claim 1, wherein the pyrophosphate is a member of the class consisting of an alkali metal pyrophosphate and ammonium pyrophosphate.

3. The process as claimed in claim 2, wherein the pyrophosphate is an alkali metal pyrophosphate.

4. The process as claimed in claim 3, wherein the pyrophosphate is at least one of potassium pyrophosphate and sodium pyrophosphate.

5. The process as claimed in claim 3, wherein the pyrophosphate anion content is from about 1.5 to about 5.5 percent.

6. The process as claimed in claim 5, wherein the pH of the bath exceeds 9.5.

7. The process as claimed in claim 6, wherein the pH is from about 10 to about 11.

8. The process as claimed in claim 1, wherein the Watersoluble pyrophosphate is the only solute in the bath.

9. The process as claimed in claim 2, wherein the voltage is under about 7.

10. The process as claimed in claim 9, wherein the voltage is from about 3 to about 5 volts.

11. The process as claimed in claim 2, wherein the current density is under about 2 amperes per square foot.

12. The process as claimed in claim 11, wherein the current density is under about one-half ampere per square foot.

13. The process as claimed in claim 1, wherein the electrolysis bath is contained Within confining walls which are an electric conductor and serve as the cathode, and an elongated rigid anode inert to the bath under the operating conditions is mounted for rotation about its own axis within said bath and at an angle of less than about 45 degrees to horizontal; and said starting copper consists of a plurality of pieces of it which are enclosed within perforated continuous confining surfaces encircling and spaced away from said anode as a shaft and rotatable with it, and with said confining surfaces having opposed ends with a separate one of opposed ends of said shaft protruding through its respective opposed end of said confining surfaces and thereby enclosing said pieces of said copper; said anode shaft being so positioned to be contacted by said copper pieces and for them to be submerged in the bath as said shaft is rotated; and rotating said shaft whereby said copper pieces are tumbled about within said confining surfaces, thereby depositing loosely adhering finely divided copper on and about the cathode; and separating said finely divided copper from said bath.

References Cited UNITED STATES PATENTS 2,578,898 12/1951 Orlik 204-l46 2,596,307 5/l952 Staufier 204-l46 3,272,729 9/l966 Jumer 204-1405 JOHN H. MACK, Primary 'Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R. 2042 1 6 

